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Old 11-03-2014, 09:24 AM
kevxs kevxs is offline
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the quest for better MPG

So I've had a great riding season but not satisfied with getting 22mpg! My route is all city miles which doesn't help but I'm pretty conservative with the throttle and feel like I should be getting better mileage.

My plugs look fine, colortune looks decent but my exhaust smells pretty bad (like i'm running too rich), other than that the bike runs great.

I did notice during a couple weeks when I was riding on the highway my MPG went up (obviously) but even stayed better for a couple tanks after I went back to city driving (like the highway miles cleaned/cleared out the engine/carbs or something).

All I can think to do is another carb clean, maybe check resistance of breaks (rear tire feels slightly stiff, will only continue to spin about 3/4 of a turn when I spin by hand on the centerstand)

does anyone have any ideas for me?
has anyone had significant MPG gain by doing the ZRX carb swap?

i will double check the plugs sometime soon, its honestly been a few months since I looked at em.

thanks!
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  #2  
Old 11-03-2014, 09:41 AM
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donebysunday donebysunday is offline
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Quote:
Originally Posted by kevxs View Post
So I've had a great riding season but not satisfied with getting 22mpg! My route is all city miles which doesn't help but I'm pretty conservative with the throttle and feel like I should be getting better mileage.

My plugs look fine, colortune looks decent but my exhaust smells pretty bad (like i'm running too rich), other than that the bike runs great.

I did notice during a couple weeks when I was riding on the highway my MPG went up (obviously) but even stayed better for a couple tanks after I went back to city driving (like the highway miles cleaned/cleared out the engine/carbs or something).

All I can think to do is another carb clean, maybe check resistance of breaks (rear tire feels slightly stiff, will only continue to spin about 3/4 of a turn when I spin by hand on the centerstand)

does anyone have any ideas for me?
has anyone had significant MPG gain by doing the ZRX carb swap?

i will double check the plugs sometime soon, its honestly been a few months since I looked at em.

thanks!
I thought I was getting bad mileage, I was getting 28-30 but this was all around. My plugs are white, no little silver specks (showing the piston burning up).
My rear wheel was maybe a little more free than yours, not much.

I was getting better mpg. with 4-1 (don't know what kind) and pod filters and the plugs had a little color too. Then I switched to stock head pipes with Dunstall reps. and stock air box with K&N, mpg. dropped and plugs turned white.
Should have happened just the opposite when I switched ? ? ?
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  #3  
Old 11-03-2014, 09:43 AM
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jetmechmarty jetmechmarty is offline
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It ain't right. 22 mpg is too far off. Does the gasoline leak every time you park it. Maybe that's funny, but you had best check on it. I gained three or four mpg just getting more voltage to the coils. Clean all the electrical contacts, if you haven't already, and pay particular attention to the ignition switch and the kill switch.

After taking care of that, how long have you had this problem? Are you properly jetted? How about float height? Are you running with the choke on? Are your plugs black and sooty? I have sooty plugs and get 30 mpg.
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Old 11-03-2014, 09:51 AM
crazy steve crazy steve is offline
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I doubt a carb swap will do anything for you. These have never been known for their fuel economy (I got 40mpg once when my '78 was still fairly new), but 22 in-town is a bit low. You say you're riding 'conservatively', you might try running at slightly higher RPMs around town, keeping the RPM at or slight above 2000. The early motors have less low-end grunt because of the hotter cams, so running the motor slow would need larger throttle opening. You might also check your jetting; if you're running bigger-than-stock jets, that could be a factor.

Even so, mid 20s in town isn't out of line for one these.
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  #5  
Old 11-03-2014, 10:27 AM
motoman motoman is offline
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Quote:
Originally Posted by jetmechmarty View Post
It ain't right. 22 mpg is too far off. Does the gasoline leak every time you park it. Maybe that's funny, but you had best check on it. I gained three or four mpg just getting more voltage to the coils. Clean all the electrical contacts, if you haven't already, and pay particular attention to the ignition switch and the kill switch.

After taking care of that, how long have you had this problem? Are you properly jetted? How about float height? Are you running with the choke on? Are your plugs black and sooty? I have sooty plugs and get 30 mpg.
+1 on all of the above......specificly the first paragraph!. These are 38-42+mpg bikes all day long when ALL issues are eliminated.
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Last edited by motoman; 11-03-2014 at 10:30 AM.
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Old 11-03-2014, 10:49 AM
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End user comment

I am absolutely mechanically uninfluenced, and I have no valuable input regarding the particulars of my floats/jets/etc. I am set up with the stock air filter. I actually rather neglect the maintenance schedule, with the exception of oil changes.

What I can comment on is my 35+ mpg that I've been getting since I bought my current XS, 32K miles ago. My highway mileage is close to 40 mpg. All I can say is, I run the fire out of her. I'm almost always above 4K rpm. I get to the highest unticketable speed I can, as fast and as I safely can. And I ride almost every day. So, maybe my XS responds better to being treated like a sports bike, and not a cruiser.
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Old 11-03-2014, 11:00 AM
kevxs kevxs is offline
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no fuel leak, i'm pretty sure I have stock jets, they are the same jets I had when I used to get 28mpg, haven't changed them.
I just pulled a couple plugs, they are on the darker side but not sooty (they look pretty good to me).

I cleaned all the electrical last season, guess i could always to it again.

I do tend to keep the rpms low, usually between 2000 - 3500

I will give it a carb clean next season, god forbid I go 3 seasons without pulling the carbs off!!

does everyone reek like exhaust fumes after a ride or is it just me?
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Old 11-03-2014, 11:18 AM
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Quote:
Originally Posted by kevxs View Post
does everyone reek like exhaust fumes after a ride or is it just me?

It's you. You aren't getting adequate burn.
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Old 11-03-2014, 11:36 AM
kevxs kevxs is offline
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so i should check the ignition system to address the incomplete burn situation? maybe new coils? (assuming my electrical connections are clean working perfectly)
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  #10  
Old 11-03-2014, 12:14 PM
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jetmechmarty jetmechmarty is offline
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Yes! Check rich condition next.
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Old 11-03-2014, 01:24 PM
motoman motoman is offline
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Originally Posted by kevxs View Post
so i should check the ignition system to address the incomplete burn situation? maybe new coils? (assuming my electrical connections are clean working perfectly)
Maybe start with a baseline voltage check at battery with ignition on. Having seat and tank off, next, check voltages at coil connections/plug-ins, same 'key-on' scenario. Should read the same. Bettin' you have a voltage drop there, which definitely will be a voltage drop at the lower rpm ranges where charging isn't at its fullest. Cruddy contacts at ignition switch and kill switch are major cause with large plug-in behind fuse panel close behind as voltage drop issues.
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Last edited by motoman; 11-03-2014 at 01:26 PM.
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Old 11-03-2014, 08:10 PM
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Kevin

I like Marty recently did all of my electrical connections using Deoxit and it did make a slight improvement in mpg. It is worth the time and effort and will improve the overall performance of the bike. I would also spend some time on the master cylinders and brakes. These bikes don't have the best brake systems on them to begin with and if they are dragging heating up then that will also cause mpg to drop. One other thing I would do is get some sea foam or mechanic in a bottle from home depot and try that in the gas. Run it and let that sit in the carbs a couple of days. Do this a couple of times. You might only have slight deposit buildup and doing this may save you from having to pull the carbs... especially for a daily rider. One question... what condition is the inside of your gas tank in. Any rust? If there is you might want to check your petcock filters and if bad put some inline filters on. If tank is in bad condition it would cause problems in the carbs if debris is passing through to them. JAT.
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Old 11-04-2014, 07:00 AM
TADracer TADracer is offline
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If everything else is right as you say then it sounds like a weak spark and/or wrong plug heat range to me. Are you still running the stock coils? if you are then check them out because they are 35 years old now and will deteriorate over that amount of time. If you have aftermarket coils then check that ohm requirement on the coils and see if the ballast resister should be in there. the resistor inline with many aftermarket 3 ohm coils will give a weak spark making exactly the conditions you describe.

Also, check spark plug heat range. If you do not have a set of stock plugs (NGK BP-6ES) installed, try a set and see if that makes a difference. A lot of people like running exotic plugs or automotive plugs and sometimes that can lead to the conditions you describe.

AS for the ZRX carb swap, I have done that and yes you may get ever so slightly better mileage (nothing astounding) but then everything else still must be right. The ZRX carb swap is a good bang for the buck but to realize anything from the swap your bike needs to be in top notch tune in all other aspects. There is no magic bullet when it comes to carbs for these bikes and you will find that using correct plugs and parts along with a very balanced tune-up are the keys to performance and mileage.

BTW, I average 38-42 MPG with the ZRX carbs in mixed riding...but then I got nearly that with the old Mikunis too.
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  #14  
Old 11-05-2014, 09:21 AM
kevxs kevxs is offline
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thanks for the input guys, i have done the dexoit job a couple of times over the last 2 seasons, i'm running the stock plugs (BP-6ES) and my gas tank is nice and clean inside. I also ran a bunch of seafoam through it early in the season hoping that would help (i think it did slightly).

That being said inline fuel filters have been on my to do list since I got the bike so I still plan on installing them at some point (and replace all the fuel lines while I'm at it).

I am running stock coils and wires, I had 'upgraded' to the black ones from mikeXS a few years ago only to have one fail and force me to limp home on 2cyls. Needless to say I put the old ones back on (with the ballast resistor, glad i kept it!). Can someone send me a link to whatever new coils are recommended? (preferably a Canadian friendly vendor).

My plans for spring are to upgrade the ignition system (new coils/wires) and brake system (stainless lines, anyone got a good link for that?)

Also I will do the diagnostic check recommended by motoman and post my results.

thanks again! this bike is pretty bulletproof, I just want it working to its full potential.
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  #15  
Old 11-05-2014, 09:40 AM
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donebysunday donebysunday is offline
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Quote:
Originally Posted by kevxs View Post
thanks for the input guys, i have done the dexoit job a couple of times over the last 2 seasons, i'm running the stock plugs (BP-6ES) and my gas tank is nice and clean inside. I also ran a bunch of seafoam through it early in the season hoping that would help (i think it did slightly).

That being said inline fuel filters have been on my to do list since I got the bike so I still plan on installing them at some point (and replace all the fuel lines while I'm at it).
Anyone have anything to say for Marvel Mystery Oil ? I swear I can tell when the bike needs another dose.

When you install the in-line filters see if you can get them in a position where they act as sediment bowls. I remember sediment bowls from my grandfathers tractors.
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